Update docs about desktop-browser integration

[dani-garcia]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-14402

📔 Objective

With the recent IPC changes and developer experience improvements around biometrics, the documentation should be updated to match.

• The IPC proxy is not baked in the application anymore, but is a separate binary that is included with the application.
• MacOS in dev mode can use IPC without requiring an App Store build or disabling Gatekeeper now, so I've removed the warning.
• The desktop app can autodetect the installed developer-mode browser extensions and add them to the manifests. Rewrote the instructions around that part and moved the Build the Desktop app section before the Add the Extension ID for Native Messaging section, which now should only be done manually as a last resort if the autodetection doesn't work.

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation
  team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed
  issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes